Actuators are used in a number of industries and applications, from elevators and automotive jacks to construction equipment and robots. Hydraulic fluid actuators, or fluid actuators, generally operate by converting fluid pressure into linear motion. Fluid actuators generally utilize a liquid, such as hydraulic oil, or a gas, such as air, as the operating fluid for converting the fluid pressure into motion.
To illustrate the operation of a typical fluid actuator, the operation of a surface controlled subsurface safety valve as used in the oil and gas industry is described. A surface controlled subsurface safety valve is generally located deep in a producing well as part of a production tubing string. The subsurface safety valve acts as a downhole flow control device to block well fluid flow during emergency conditions. The subsurface safety valve is generally controlled from the well surface by the application of hydraulic pressure to the subsurface safety valve.
Hydraulic pressure is communicated through a high pressure line to a fluid actuator contained within the subsurface safety valve. A biasing system contained within the subsurface safety valve produces a force on the fluid actuator to compress the fluid actuator. When fluid pressure from the well surface is applied, the fluid actuator overcomes the force exerted by the biasing system and extends the fluid actuator and opens the subsurface safety valve to allow well fluid to flow through the subsurface safety valve to the well surface. Upon removal of the fluid pressure from the well surface, the load exerted by the biasing system compresses the fluid actuator, and closes the subsurface safety valve to block the flow of well fluid to the well surface.
Conventional fluid actuators are often prone to damage due to contamination from the environment. For example, in the case of fluid actuators used in subsurface safety valves, the high pressure/heat environment in addition to the caustic chemicals found in the well can damage the seals within the fluid actuator. Accordingly, the control fluid may be contaminated with environmental contaminates and the control fluid may leak from the fluid actuator.
Conventional fluid actuators often have seals fabricated with plastics that are prone to wear during use. Accordingly, the fluid actuator must be removed from service and disassembled to replace the seals. Depending upon the application, removal and replacement of the fluid actuator can be extremely expensive.